The present invention relates to a general-purpose measuring apparatus for measuring grooves positions of a workpiece which is capable of measuring grooves on a workpiece such as twisted grooves, equal split grooves and unequal split grooves, and determining the center positions of said grooves, and determining the twist directions of grooves having twist angles in alternatingly reverse directions.
Determination of the center positions of a grooves formed at the outer surface of a workpiece is required to machine such grooves by grinding, chamfering and the like. Usually, such determination is accomplished by an operator based on dimensions shown in drawings. If such determining operation can be automated, the groove measuring time can be shortened and production cost can be decreased by reducing the number of personnel required. Thus, development of an apparatus capable of automatically measuring such grooves is desirable. If an apparatus is developed which is applicable to a variety of grooves, such as a twisted groove, equal split groove, unequal split groove and many others, it is expected that the efficiency of the measuring operation will be greatly improved.
To grind twisted grooves formed at the outer surface of a cylindrical workpiece, such as an inner race of constant velocity joint, the positions of twisted grooves are required to be detected accurately by measurement, so that the twisted grooves are indexed to a location corresponding to the position of a grinding wheel.
However, in cases where each of twisted grooves has the same twist angle, but their twist direction change alternatively, it is difficult to measure their positions accurately, as is explained hereinafter.
Conventionally, the center positions of twisted grooves of a workpiece supported on a grinding machine are measured using a sensor which is disposed in a plane perpendicularly intersecting the rotational axis of the workpiece and corresponding to the longitudinal center of grooves.
However, actually it is very difficult to set the detecting center of the sensor in the place corresponding to the longitudinal center of twisted grooves, and there can be produced some dislocations.
For example, as shown in FIG. 12, assuming that the erroneous dislocation between the detecting center of sensor 7 and the plane corresponding to the longitudinal center of workpiece 1 is a, and the twist angle of twisted grooves is .alpha., the dislocation .delta. represented by a . tan .alpha. occurs in the circumferential direction of the workpiece 1 as an error. To eliminate said dislocation .delta., the sensor 7 is required to be set at higher accuracy in the plane perpendicular to the rotational axis, and is therefore required to be set by skilled workers. This was an obstacle to automatize the preparing operation for measurement.
When finishing grinding, chamfering machining or the like is carried out for each of the grooves formed at the outer periphery of a workpiece, it is usual that such machining is performed in order of the groove arrangement starting from a certain groove of the workpiece. Consequently it is required to index each groove exactly from a predetermined reference position. For this purpose, in automatic grinders or the like, angular position of the center of each groove with respect to the reference position indicated on the manufacturing drawing is previously inputted as set data, and in accordance with the set data each groove is automatically indexed, then the grinding or the like is carried out.
However, when the center positions of the grooves are indexed in accordance with the set data for grinding operation, as mentioned in the above description, the grinding allowance to both sides of the groove is different in each groove because of pitch errors among the center positions of the grooves formed on the workpiece. As a result, there is a problem that the different grinding resistances acting on both the sides of the grinding wheel exert a bad effect upon the grinding accuracy, or shorten the life of the grinding wheel.
Further, when the measurement of the groove positions is carried out by operators as described above, the efficiency of the machining operation is low because it takes long time for the measurement. In addition, when a plurality of grooves and lands are alternately formed with a regularly periodic pattern on the outer periphery of the workpiece, it is not necessary to measure those positions of all grooves on the workpiece, because it is possible to derive the positions of all grooves by measuring part of the grooves with said periodic pattern.